Coal and crude oil are two of the most important fossil fuels in use in the world today to satisfy our energy needs. Particularly in countries like the U.S. and China, where there are enormous deposits of coal in their land, mining of coal is even more important, if not indispensable. No doubt the acquisition of other energy sources such as gas and crude oil also involves dangerous everyday operations, but coal mining has to take the top spot as far as the number of workers that perish every year is concerned. It is believed that explosions in mines alone inside China have claimed more than half a million lives during the past decade. Although the number of miners killed elsewhere in the world during mining operations is far less than those reported inside China, the number still runs into many thousands every year.
The cause of explosions inside mines has become fairly well understood over the years. The presence of methane gas (CH4) pockets is known to exist and scatter unpredictably among rocks containing coal deposits. Methane gas is odorless and the lower explosion limit (LEL) of methane gas is around 5.0 volume percent in air containing ˜21 vol. % of oxygen. It is generally believed that underground mine explosions are caused by miners accidentally and unknowingly hitting a methane gas (CH4) pocket in the mine while they are crushing and churning rocks by hand or with massive machines to get to coal deposits in tunnels. Without knowing the existence of an explosive air mixture in their work area so as to stop working immediately, the miners' operation continues to generate sparks that ultimately lead to the unfortunate explosion. Such underground mine explosions could surely be prevented if only the miners knew that immediate ambient air they are breathing has reached a lower explosion limit (LEL) for methane gas and they have to immediately stop operating their machines or rock churning by hand in order not to generate any sparks that could set off an explosion. Although methane gas sensors can detect LEL concentration levels for methane gas when such sensors are stationed at adequate distances inside mine tunnels, it is not always the case that such a sensor is in the immediate vicinity of the space where the miners are doing the heavy work. Without the presence of such a methane sensor in the space to warn the miners of such a dangerous situation where they work, underground mine explosions will inevitably occur from time to time causing the lives of many miners every year.
It has long been understood and believed that in order to eliminate the danger of underground mine explosions caused by the methane gas, one has to fulfill two important monitoring functions for mines. The first is an integrated communication and tracking system designed specifically for use in underground mines. Such a system not only is able to continuously track the exact whereabouts of the miners underground, it is also capable of monitoring in real time the outputs of all the installed gas sensors stationed inside the mine in order to be able to assess at all times any dangerous levels of gas built-ups at locations that might trigger an explosion. Over the past decade a small number of such integrated communication and tracking systems have become available. Within the last couple of years, some of them have even been installed for testing in a small number of mines around the world. For tracking individual miners working underground, an effective way is to install wireless location sensors in the helmets of miners that communicate directly with the central system above ground. The whereabouts of individual miners underground can now be continuously tracked and notified if necessary to evacuate from specific locations in case of potential danger.
But while the availability of such an integrated communication and tracking system for mines is a necessary requirement for eliminating the danger of underground mine explosions, it is not sufficient by itself to eliminate such danger. The reason is relatively straightforward. Although an expertly functioning communication and tracking system can pin point the location of a potentially explosive environment via monitoring of a fixed system of methane sensors strategically scattered throughout the tunnels of the mine, it cannot follow the exact locale of a crew of miners underground at work. If the crew cannot sense the danger of an explosive environment they find themselves in while they are working, an explosion can still occur. However, if the crew is provided with means to accurately and reliably detect the dangerous level of methane in their midst, they can immediately take action to avoid the possibility of explosions and evacuate the site. Meanwhile the central system can also take note of the dangerous condition at this location and notify other miners nearby to evacuate until the environment is under control and is safe again.
The ability of an integrated communication and tracking system for mines to pin point the whereabouts of every miner working underground can be achieved via installation of a wireless location sensor in the helmet of each of these miners. Imagine that the helmet of every miner working underground is also equipped with a wireless and intrinsically safe methane sensor capable of accurately detecting a dangerous level of methane (like the LEL) in the vicinity of working miners; in this scenario, the second important monitoring function necessary and sufficient to eliminate the danger of underground mine explosions mentioned will be fulfilled.
However, despite a long felt need for increased mine safety, and the imperative of saving miner's lives, an integrated communication and tracking system for mines does not yet exist, at least not with a methane sensor that can adequately function in such a system. This invention fulfills this long felt need by providing an intrinsically safe methane sensor that satisfies the criteria necessary for a methane sensor to be effectively and economically integrated into a communication and tracking system for mines.